Drives for centrifugals



R. C. GOODWIN DRIVES FOR CENTRIFUGALS March 19, 1963 5 Sheets-Sheet 1Filed Oct. 18, 1960 A sE INVENTOR RALPH c. eooowm ATTQlEY March 19, 1963R. c. GOODWIN 3,081,598

DRIVES FOR CENTRIFUGALS Filed Oct. 18, 1960 5 Sheets-Sheet 5 V v as M4-INVENTOR. f I RALPH c. eooowm L ATTORNEY.

March 19, 1963 R. c. GOODWIN 3,081,598

DRIVES FOR CENTRIFUGALS Filed Oct. 18, 1960 5 Sheets-Sheet 4 INVENTORRALPH C. GOODWIN ATTOR Y March 19, 1963 R. c. GOODWIN 3,

DRIVES FOR CENTRIFUGALS Filed Oct. 18, 1960 5 Sheets-Sheet 5 x Q Q 55g 3Eg D P/L OTED PEL/EF PILOTED PE4/EF 8 INVENTOR. RALPH c. eooowm ATORNEY.

United States Patent 3,081,598 DRIVES FOR CENTRIFUGALS Ralph C. Goodwin,Hamilton, Ohio, assignor to The Western States Machine Company,Hamilton, Ohio, a corporation of Utah Filed Get. 18, 196i), Ser. No.63,368 43 Claims. (CI. 60-53) The present invention relates generally toheavy duty rotary drive assemblies, and more particularly is directed todrives for centrifugals or extractors of the kind used for removing orseparating liquids from bulk solids, for example, as in the chemicalindustry or in the refining of sugar, or for removing excess water orother liquid cleaning agents from clothing and other fabrics inlaundries and cleaning establishments.

The basket of a centrifugal or extractor of the described character isfrequently driven by an electric motor directly coupled to the basketshaft, or by a belt and pulley transmission from an electric motor whichis ofiiset relative to the basket shaft. Frequently the basket isrotatably supported by a structure that permits gyratory movement of thebasket in the event of unbalanced loading thereof, thereby to avoid thetransmission of vibrations to the fixed supporting structure of thecentrifugal, and the provision of an electric motor for driving thebasket makes the relatively large mass of the motor a part of theassembly undergoing gyratory movement, and thereby further increases thevibratory energy that needs to be absorbed. Further, if the large massof the electric motor is offset relative to the basket shaft and therotary drive is transmitted to the basket shaft by way of a belt andpulley transmission, the suspended mass is not symmetrical about theaxis of the basket so that an elliptical gyratory movement results fromunbalanced loading of the basket, and such elliptical gyratory movementgives rise to undesirable tilting of the basket axis.

The use of an electric motor for rotating the basket of a centrifugal ofthe described character generally requires the positioning of the motorabove the basket if the latter is to be provided with a bottom dischargefor solids, as an electric motor having a sufficiently large output todrive the basket will have relatively large dimensions and thereforetake up the space required for the bottom discharge when it is directlycoupled to the basket shaft below the basket. On the other hand, if therelatively large electric motor is disposed to one side of the basketand the rotary drive is transmitted to the lower end of the basket shaftbelow the basket by way of a belt and pulley transmission, thetransmission belts present a maintenance problem, and braking of therotation of the basket is less reliable than with a directly coupleddrive. Further, the conventional overhead drives of centrifugal basketstend to disadvantageously increase the height of the centrifugal, andthereby limit the building structures in which such machines can beinstalled. The overhead drives also clutter the space above thecentrifugal basket, thereby interfering with the performance ofoperations around the basket curb, and, in vapor tight machines, thereis the problem of sealing the spindle or shaft opening in the curb top.

Accordingly, it will be seen that a desirable drive for centrifugals orthe like should provide a driving component directly coupled to thebasket shaft and having relatively small mass and dimensions symmetricalwith respect to the basket axis so that the basket can be suspended forgyratory movement in the event of unbalanced loading thereof withouthaving such driving component adversely affect the conditions of thegyratory movement. Further, such a driving component can be disposedbelow the basket without interfering with the bottom discharge of solidsfrom the basket. Where the 3,081,598 Patented Mar. 19, 1963 icecentrifugal is provided with a discharger of the kind havmg a shoe whichremains within the basket, for example, as disclosed in United StatesLetters Patent No. 2,667,974, issued February 2, 1954, to JosephHertrich, the centrifugal drive should also be capable of rotating thebasket at a high speed in one direction during normal centrifuging ofthe solids, and of rotating the basket in the opposite direction, at arelatively slow controlled speed, during discharging of the solids, sothat, with the shoe of the discharger extending generally in thedirection of the high speed rotation, the shoe can dig into the wall ofsolids only during discharging and can be safely maintained in thebasket during centrifuging.

It is an object of the present invention to provide a drive forcentrifrugals or the like having the above described advantageouscharacteristics.

In accordance with an aspect of this invention, a drive for centrifugalsor the like includes a hydraulic, positive displacement motor directlycoupled to the shaft of the basket or other assembly to be rotated, anda remote power unit including an electric motor, or other prime moverdriving at least one hydraulic pump by which hydraulic fluid underpressure is fed through conduit-s to the positive displacement motor forthe purpose of operating the latter.

A hydraulic drive of the described character has the advantages ofproviding speed adjustment, constant horsepower or constant torqueacceleration, forward and reverse rotation at different speeds andhydraulic braking of the driven assembly, in a less expensive drive thanis otherwise available. Further, the relatively small size and mass ofthe hydraulic motor make it possible to position the motor under thebasket and to directly couple the motor to the basket shaft in acentrifugal of the link suspended type. Even when applied toaconventional overhead suspended type centrifugal, the small dimensionsof the hydraulic motor reduce the head room requirements.

It is a more specific object of the invention to provide a hydraulicdrive for centrifugals or the like which is capable of effecting highspeed forward rotation, for example, during spinning of the centrifugalbasket, and also capable of braking such high speed forward rotation sothat the basket is rapidly brought to a standstill and thereafter rotatd at a relatively slow constant speed in the reverse direction, forexample, during the discharging of solids from the basket.

Further objects are to provide hydraulic drives of the describedcharacter wherein small valves exert pilot control over large oil flows,and power peaks are maintained gelatively low while minimizing heatingof the hydraulic uid'.

In accordance with another aspect of the invention, first and secondconduits extend from the power unit to the hydraulic motor, and controlsare provided to direct the how of hydraulic fluid under pressure throughthe first conduit to the motor and return the exhausted fluid from themotor through the second conduit during high speed forward rotation, andto direct fiuid under pressure to the motor through the second conduitfor return from the motor through the first conduit during relativelyslow reverse rotation, the first and second conduits having pres surerelief means associated therewith in order to prevent the build-up ofexcessive pressures therein, particularly during braking of the rotationof the motor. Thus, if the motor is initially effecting high speedforward rotation of the centrifugal basket, and the controls are thenshifted to the position for braking and reverse rotation, the hydraulicmotor initially acts as a pump and the pressure relief means associatedwith the second conduit establishes a limited back pressure in thelatter which acts in the hydraulic motor to produce a predeterminedbraking torque until such time as the motor comes to a standstill andhydraulic fluid under pressure flows through the second conduit to themotor for effecting reverse rotation.

Since hydraulic, positive displacement motors of the type to be employedhave leakage losses which progressively increase with increasing loadson the motor during slow rotation of the latter, the feeding ofhydraulic fluid under pressure to the motor at a constant flow rateduring the slow reverse rotation of the basket would result in aprogressively decreasing speed of reverse rotation as the load on themotor increased, for example, as a result of the action of thedischarging shoe cutting into the wall of solids in the basket.Accordingly, it is another object of the invention to provide acentrifugal drive of the described character wherein the rate of flow ofhydraulic fluid under pressure to the motor during the relatively slowreverse rotation of the centrifugal basket is increased, either in astep-by-step or progressive fashion, in response to increases in thepressure of the hydraulic fluid, that is, in accordance with increasingload on the hydraulic motor thereby to maintain a substantially constantspeed of reverse rotation.

A still further object of the invention is to provide a hydraulic drivefor centrifugals or the like wherein means are provided for avoidingcavitation within the hydraulic motor as a result of the failure tomaintain an adequate supply of hydraulic fluid to the motor in the eventof a power failure while the basket is being rotated.

The above, and other objects, features and advantages of the invention,will be apparent in the following detailed description of illustrativeembodiments thereof which is to be read in connection with theaccompanying drawings forming a part hereof, and wherein:

FIG. 1 is a schematic view of a hydraulic drive for a centrifugal inaccordance with a first embodiment of the present invention;

FIG. 2 is an enlarged, diagrammatic sectional view of a control valveincluded in the hydraulic drive of FIG. 1;

FIG. 3 is a view similar to that of FIG. 2, but showing the valve inanother operating position;

FIG. 4 is also a view similar to that of FIG. 2, but showing the controlvalve in still another operating position;

FIG. 5 is a vertical sectional view of a variable volume hydraulic pumpincluded in the hydraulic drive of FIG. 1;

FIG. 6 is a schematic view of a portion of a hydraulic drive forcentrifugals which is a modification of the drive illustrated in FlG. 1;

FIG. 7 is an enlarged elevational view, partly broken away and insection, of a flow control device included in the modified drive of FIG.6;

FIG. 8 is a schematic view of a hydraulic drive for centrifugals or thelike constructed in accordance with another embodiment of the invention,and with a control valve included therein being shown in section;

FIG. 9 is a schematic view of a portion of a hydraulic drive forcentrifugals which is a modification of the hydraulic drive of FIG. 8;

FIG. 10 is a schematic view showing another modification of the drive ofFIG. 8; and

FIG. 11 is a schematic view of a hydraulic drive for centrifugals or thelike constructed in accordance with still another embodiment of theinvention.

Referring to the drawings in detail, and initially to FIG. 1 thereof, itwill be seen that a hydraulic centrifugal drive embodying the presentinvention, and there generally identified by the reference numeral 10,includes an electric motor 11 which maybe mounted on the top of ahydraulic fluid storage tank 12, and which has the opposite ends of itsshaft 13 connected, by couplings 1d and 15, respectively, to a mainhydraulic pump it? and to an auxiliary hydraulic pump 17, with the pumps16 and 17 h also being mounted on top of tank 12 so as to provide acompact power unit.

The relatively large main pump 16, which is intended to supply thehydraulic fluid under pressure for effecting the high speed forwardrotation of the associated centrifugal basket or the like, is preferablyof the type delivering a variable volume of fluid that is automaticallyadjusted in accordance with the demands of the circuit to which it isconnected, for example, a pump of the type available from RacineHydraulics and Machinery Inc, Racine, Wisconsin, under the designationRacine Model R Variable Volume Vane Pump. As shown in FIG. 5, such apump may include a housing 18 with a shaft 19 mounted rotatably thereinand supporting a rotor 29 having radial slots 21 slidably accommodatingvanes 22 which are spring urged radially outward into sliding contactwith the inner cylindrical surface of a shiftable inner casing 23. Theinner casing 23 is suspended, from the top, by an assembly 24 and ismovable horizontally with respect to the axis of shaft 19 from aposition where the center of the inner cylindrical surface of casing 23is aligned with the axis of shaft 19 to a position where there is amaximum eccentricity between the axis of shaft 19' and the center ofcasing 23. The pump housing 18 has a cylindrical extension 25 at oneside, and a piston 26' is axially slidable in the extension 25 and isurged against the shiftable casing 23 by a governor spring 27 whichbears against an adjustable abutment 28 carried by a screw 29 extendingthreadably through the outer end of extension 25.

It will be apparent that the spring 27 and piston 26 tend to shiftcasing 23 to a position of maximum eccentricity with respect to the axisof shaft 19, and a stop screw 36) extends threadably into housing 18 ata location diametrically opposed to piston 26 and is engageable bycasing 23 for adjustably limiting the shifting move ment of the casingby spring 27.

The pump 16 is providel with an inlet 31 which receives fluid to bepumped from tank 12 by way of an inlet pipe 32 depending into the tank(FIG. 1), and the pump 16 further has an outlet 33 for delivering thehydraulic fluid under pressure. If it is assumed that shaft 19 isrotated at a substantially constant speed, it will be apparent that thevolume enclosed between successive vanes 22 of the pump will be amaximum, and the fluid will be pumped at a maximum volumetric rate whenthere is a maximum eccentricity between the center of casing 23 and theaxis of shaft 19. However, the pressure of the fluid being pumped actsagainst the inner surface of the casing 23 so that, when the outputpressure is at a maximum, such pressure shifts casing 23 in thedirection opposed to the force exerted by spring 27, thereby moving thecenter of casing 23 toward the axis of shaft 19 and correspondinglydecreasing the volumetric rate at which the fluid is pumped. Therelationship between the pressure of the pumped fluid and the volumetricrate at which the fluid is delivered is determined by thecharacteristics of the governor spring 27 and, in the illustratedembodiment of the invention, the governor spring 27 has been selected soas to maintain a substantially constant horse-power demand on theelectric motor 11. Thus, spring 27 provides for the delivery ofhydraulic fluid at a high pressure when the demand of the circuit orsystem is for a relatively low volume of fluid, thereby to provide agood acceleration torque, and to deliver the fluid at a relatively lowpressure which provides an adequate torque for high speed spinning ofthe centrifugal basket, when there is a demand for the delivery of thefluid at a high volumetric rate during such high speed spinning.

It will be apparent that adjustments of the screw 29 can shift the rangeof pressures delivered by the pump to higher or lower levels, but willnot basically alter thev pressure-volume relationship established byspring 27, whereas adjustment of the screw 30, which controls themaximum travel or shift of the casing 23, can vary the. upper limit ofthe volumetric rate at which hydraulic fluid;

is delivered, and thus the top speed of the centrifugal basket.

The output 33 of pump 16 is connected to a pipe or conduit 34 (FIG. 1)which has a piloted relief valve 35 interposed therein. The pilotedrelief valve 35 serves the dual function of limiting the pressure withinpipe 34- and of unloading the related pump 16 when the output of thelatter is not required for driving the associated centrifugal basket,and a piloted relief valve having such dual functions may be obtainelfrom the Denison Engineering Division, American Brake Shoe Company,Columbus, Ohio, under the designation RV40. Piloted relief valve 35 isalso connected to a pipe 36 which opens into a return pipe 37 extendingback to tank 12 and through which the output of pump 16 is dumped backto the tank when such output is not required, for example, when thecentrifugal basket is being rotated in the reverse direction ashereinafter described in detail, or through which hydraulic fluid isdumped when the pressure in pipe 34 exceeds a predetermined, adjustedvalue for which the piloted relief valve 35 has been se. A pilot line 38extends from valve 35 and loads the latter to limit the pressure in pipe34 to a predetermined value, for example, to a pressure set at 1000 to1250 pounds per square inch when the pilot line 38 is blocked, while thevalve 35 is unloaded and effective to dump the output of pump 16 whenpilot line 38 is open or unblocked.

Pipe 34 is connected, for example, by a coupling 39, to a flexible pipeor hose 40 which extends to the inlet 41 of a hydraulic, positivedisplacement motor 42, for example, a vane type motor of the kindavailable from the Denison Engineering Division, American Brake ShoeCompany, Columbus, Ohio, under the designation THES'C. The identifiedmotor is operated by a flow of hydraulic fluid of up to forty gallonsper minute at a pressure of up to 1250 pounds per square inch duringrotation in the forward direction, that is, when fluid under pressure issupplied thereto through the inlet 41, and such motor is intended toreceive fiuid under pressure at a relatively small volumetric rate, forexample, 5.7 gallons per minute, and at a relatively high pressure, forexample, approximately 2000 pounds per square inch, when rotated in thereverse direction, that is, when fluid under pressure is suppliedthereto through the normal outlet 43 and exhausted from the motorthrough the normal inlet 41. Of the above indicated relatively smallvolu metric rate supplied to normal outlet 43, a major portion, forexample, approximately 4 gallons per minute, eifects the reverserotation, while the remainder of the flow supplies theleakage throughthe motor 42 at high discharging pressure.

Since the motor 42 has a relatively small mass and dimensions in termsof the power that it can deliver to a rotary element to be driventhereby, such motor is ideally suited for direct coupling to the shaftof the basket of a centrifugal which may be of the kind disclosed indetail in the copending application for United States Letters Patentidentified as Serial No. 62,713, filed October 14, 1960, by Ralph C.Goodwin and Thomas R. Laven. Such centrifugal is diagrammaticallyrepresented by broken lines on FIG. 1 and there generally identified bythe reference numeral 44, and includes a basket 45 which is open at thetop to receive the charge and has a bottom discharge opening. The basketis rotatably mounted on a shaft 46 supported in a manner to permitgyrato-ry movement of the basket when the loading of the latter isunbalanced, and the shaft of motor 42 is directly coupled to shaft 46and disposed below the basket 45 in order to leave the curb top clearand to reduce the overall height of the centrifugal, while the smalldimensions of motor 42 avoid any interference with the downwarddischarge of solids from the basket and the small mas of the motoravoids any adverse influence on the conditions of the gyratory movementof the basket.

The auxiliary pump 17 is of the type delivering the bydraulic fluid at arelatively high pressure, for example, i

2000 pounds per square inch, at a relatively small volumetric rate, forexample, approximately 5.7 gallons per minute, and may be a vane typepump available from Denison Enginering Division, American Brake Shoe Company, Columbus, Ohio, under the designation TMOI. The inlet of pump 17 iconnected to an inlet pipe '47 extending into tank 12 for withdrawinghydraulic fluid from the latter, while the outlet of pump 17 isconnected to an Outlet pipe 48 which communicates with a piloted reliefvalve 49 similar to the piloted relief valve 35, but set to relieve thepressure in pipe 48 at a higher value, for example, at a pressure of2000 pounds per square inch. Piloted relief valve 49 communicates with apipe 50 which is connected, as by a coupling 51, to a flexible pipe orhose 52 extending to the outlet 43 of motor 42,

and a pilot line .53 extends from valve 49 and causes the latter tolimit the pressure in pipes 43 and 50 to the adjusted value for whichvalve 49 is set when pilot line 53 is blocked, whereas piloted reliefvalve 49 is effective to dump the output of pump 17 into return pipe 37,by

way of a pipe 54, when pilot line 53 is open.

Pilot lines 38 and 53 are connected to a control valve generallyidentified by the reference numeral 55, and

which may be of the type having three operating positions available fromDenison Engineering Division, American Nalve 55 further includes a valvebody or spool 58 with a rod 59 extending from the spool out of housing56 for actuation by a lever 69. The lever 66 may be in the form of ahandle, as shown, for manual actuation, or it may be otherwise actuated,for example, by a solenoid or the like.

The spool 58 of valve '55 is formed so that, when in the position ofFIG. 2, both pilot lines 38 and 53 communicate with return line 57,whereby both of the piloted relief valves 35 and 49 are unloaded anddump the outputs of the related pumps 18 and 17, respectively. Withvalve 55 in the position of FIG. 2, the basket 45 connected to motor 42can either remain at rest, or, if the basket is rotating when the valveis placed in the position of FIG. 2, the basket can coast in thedirection of the existing rotation. When spool 58 of valve 55 is shiftedtoward the right from the position shown in FIG. 2 to the position shownin FIG. 3, pilot line 53 continues to communicate with return line 57,while pilot line 38 is blocked so that piloted relief valve 49 isunloaded and continues to dump the output of its related pump 17,whereas the pressure on piloted relief valve 35 builds up to the mainpump output pressure which i maintained.

With the valve in the position illustrated in FIG. 3, the output ofpunrp 16 is fed through pipe 34 and hose 4% to the inlet 41 of motor 42to cause rotation of the latter in the forward direction at a relativelyhigh speed, while the exhausted fluid is discharged through the outlet43 of motor 42, and through hose 52, pipe 50, piloted relief valve 49,pipe 54 and pipe 37 back to tank 12.

When spool 58 of valve 55 is moved further to the left from the positionof FIG. 2 to the position shown in FIG. 4, pilot line 33 is placed incommunication with return line 57 While pilot line 53 is blocked so thatpiloted relief valve 35 is unloaded and dumps the output of pump 16, andpiloted relief valve 49 is loaded and functions to limit thepressure ofthe fluid supplied from pump 17 through pipe 48. to the position of FIG.4 while the basket is in highspeed forward rotation, motor 42 acts as apump and relief valve 4% determines the value of the back pressureavailable in pipe 50 to exert a braking torque in the If valve 55 isshifted motor for arresting rotation of the basket until the latter hascome to rest, whereupon the fluid supplied under pressure by the pump 17causes relatively slow reverse rotation of the centrifugal basket.

On the other hand, if the valve 55 is shifted from the position of FIG.4, corresponding to reverse rotation or braking, as described above, tothe position of FIG. 3 corresponding to forward, high-speed rotation,the initial effect of the described system is to make thepiloted reliefvalve 35 function to limit the back pressure in pipe 34 for braking thereverse rotation of the centrifugal basket until the latter has beenbrought to rest, whereupon the normal flow is established through pipe34 in the direction from relief valve 35 toward motor 42 for effectingthe forward rotation of the basket.

The leakage characteristics of hydraulic motor 42 at low speed are suchthat the volumetric rate of delivery of hydraulic fluid to the motor hasto be increased in order to maintain a constant speed when the load onthe motor and hence the pressure of the hydraulic fluid supplied theretoare increased. Accordingly, if the hydraulic fluid is supplied to motor42 at a constant rate of flow during reverse rotation of the motor, thespeed of such reverse rotation would tend to decrease with increasedload on the motor. In order to avoid such decreasing speed of reverserotation, the hydraulic drive embodying the present invention mayfurther include two adjustable flow control valves, which may be of thetype available from Denison Engineering Division, American Brake ShoeCompany, Columbus, Ohio, under the designation VlAAO23330, and which areidentified by the reference numerals 61 and 62, respectively. The valves61 and 62 are arranged in a circuit bypassing a check valve 63interposed in pipe 50 and permitting flow through the latter only in thedirection from motor 42 toward piloted relief valve 49. The bypasscircuit includes a line 64 branching off from pipe 50 at a locationbetween check valve 63 and relief valve 49 and leading to the inlet sideof adjustable flow control valve 61, and a line 65 leading from theoutlet of valve 61 back to pipe 50 at a location between check valve 63and the connection -1 to the hose 52, so that, when the pilot line 53 ofrelief valve 49 is blocked and the output of pump 17 passes throughpiloted relief valve 49 in the direction toward motor 42, the flow ofhydraulic fluid passes through adjustable control valve 61 which is setto determine the basic speed of reverse rotation. The flow of hydraulicfluid through the other flow control valve 62 is blocked unless thepressure in the line 50 between check valve 63 and the motor exceeds apredetermined value as a result of the imposition of a relatively highload on the motor 42, at which time flow also occurs through valve 62,thereby to increase the total rate of flow of hydraulic fluid formaintaining a substantially constant speed of rotation of motor 42. Theflow of hydraulic fluid through valve 62 is controlled by a pilotoperated sequence valve 66 which may be of the kind available fromDenison Engineering Division, American Brake Shoe Compan Columbus, Ohio,under the desig nation KH-041-E06D, and which is interposed in a line 67branching off from the line 64 and leading to the inlet of control valve62, with the operation of the sequence valve being controlled by thepressure sensed by a pilot line 68 extending from pipe 50 between checkvalve 63 and motor 42. The output of flow control valve 62 is led backto pipe 50 by way of a line 69 which may be joined to the line 65extending from the flow control valve 61.

As shown in FIG. 6, the arrangement of two flow control valves 61 and 62and the sequence valve 66 in the hydraulic drive of FIG. 1 can bereplaced by a single flow control valve 61 which is continuouslyadjusted by an actuating device 76 having a pressure sensing connection77 to the pipe 65 at the downstream side of the remaining flow controlvalve 61 so that the pressure of the hydraulic fluid fed to motor 42during reverse rotation operates device 76 to cause the latter tofurther open valve 61 in response to an increase in the sensed pressure,that is, in accordance with increasing loads on motor 42.

As shown in detail on FIG. 7, the actuating device 76 preferablyincludes a cylinder 78 secured to the housing of flow control valve 61,as by a bracket 79, and having a plug 80 screwed into one end forattachment to the pressure sensing connection 77. A tube 8 1 extendsaxially from plug 80 and has an axial bore 82. A sleeve 83 is axiallyslidable on tube 81 within cylinder 78 and has an external flange 84 atthe end adjacent plug 80 with a radial pin 85 extending from flange 84through an axial slot 86 in the top of cylinder 78. A hearing bushing 87is screwed into the end of cylinder 78 remote from plug 80 and slidablyreceives the adjacent end of sleeve 83 which is closed by a screw plug88. A restriction or metering rod 89 extends axially from screw plug 88through bore 82 of tube 81 with a small radial clearance therebetween,and a helical compression spring 90 is disposed around sleeve 83 incylinder 78 between plug 87 and flange 84 of sleeve 83 so as to urge thelatter toward the right, as viewed in FIG. 7.

It will be apparent that the hydraulic fluid under pressure carried byconnection 77 passes through the annular clearance between fixed tube 81and restriction rod 89 and acts against the plug 88 to urge sleeve 83 tomove toward the left, as viewed in FIG. 7, in opposition to the force ofspring 90. Thus, when the pressure sensed by connection 77 increases inresponse to an increasing load on motor 42 during reverse rotation ofthe latter, the sleeve 83 and its radial pin 85 are displaced toward theleft.

Further, as shown in FIG. 7, the flow control valve 61, which iscommercially available from Denison Engineering Division, American BrakeShoe Company, Columbus, Ohio, under the designation VLAAO23330, aspreviously indicated, includes a rotatable knob assembly 91 foradjusting the rate of flow of hydraulic fluid through valve 61, and suchknob assembly 91 is modified by providing two spaced apart, axiallyprojecting pins 92 thereon between which the pin 85 of actuating device76 engages so that movement of pin 85 along slot 86 causes angulardisplacement of knob assembly 9.1 to correspondingly adjust valve 61 forincreasing the rate of flow of hydraulic fluid to motor 42 withincreasing loads on the latter so as to compensate for the increasedleakage through the motor and thereby maintain a constant speed ofreverse rotation.

In order to provide indications of the pressures existing in the pipes34 and 50 which feed fluid under pressure to the motor from the pumps 16and 17, respectively, a pressure gauge 70 may be connected to a centralport of valve housing 56 and, as shown in FIGS. 2, 3 and 4, the spool 58of valve 55 is formed with a central land 71 which moves to one side orthe other of the port communicating with gauge 70, so that the gaugeindicates the pressure in pilot line 38 (FIG. 3) or in pilot line 53(FIG. 4).

In order to prevent the imposition of an excessive back pressure on pump17 and overspeeding of electric motor 11 in the event of a power failureduring braking of high speed forward rotation of basket 45, a checkvalve 72 is interposed in pipe 48 between piloted relief valve 49 andthe outlet of pump 17 and permits flow of fluid through pipe 48 only inthe direction from the pump.

It will be seen that, if there is a power failure during high speedforward rotation of basket 45, the inertia of the rotating basket willcause motor 42 to act as a pump. However, the inlet 41 of motor 42 mustbe generously supplied with hydraulic fluid during such action as a pumpin order to avoid cavitation and, for this purpose, a pipe 73 extendsfrom the pipe 36 and opens into the pipe 34 at a location which isdownstream wtih respect to the piloted relief valve 35, and a checkvalve 74 is interposed in the pipe 73 and permits flow through thelatter only in the direction toward pipe 34. Thus, in the event of apower failure while control valve 55 is disposed for high speed forwardrotation of basket 45, the hydraulic fluid returning from outlet 43through hose 52, pipe Sil check valve 63, piloted relief valve 4d andpipe 54 passes through pipe 36 and the check valve 74 of pipe 73 to thepipe 34 in order to maintain an adequate'supply of hydraulic fluid atthe inlet or suction side of motor 42 acting as a pump. Since there maybe an excessive pressure drop across the check valve 74 at high rates offlow of hydraulic fluid therethrough, and this excessive pressure dropwould have the tendency of permitting some of the returned hydraulicfluid passing through the pipe to flow back to the tank through thereturn pipe 37, and thereby result in an inadequate supply of oil to theinlet or suction side of motor 42 acting as a pump, there is furtherprovided a spring loaded check valve 75 interposed in the return pipe 37and creating a resistance to the return flow of fluid through pipe 37,thereby to overcome the flow resistance of the above described checkvalve 74.

As shown in FIG. 6, the above mentioned spring loaded check valve '75may be replaced by a cooler 93 having a housing 94 with its inlet andoutlet connected to return pipe 37 so that the return flow of fluidthrough pipe 37 passes through housing M. Cooler 93 further includescoils 95 of small diameter tubing disposed in housing 9 and creating aresistance to the return flow of fluid through pipe 37, for example, apressure drop of p.s.i., which is sufficient to overcome a flowresistance of check valve 74, and water is circulated through coils 95to cool the return flow of hydraulic fluid. Thus, cooler 93 performs thefunction of the check valve 75 which it replaces and also functions asan economical and effective fluid cooler.

In order to avoid cavitation in motor 42 in the event of a power failureduring reverse rotation of basket 45, the

normal outlet 43 of motor 42 is then generously supplied with fluid byway of pipe 96 (FIG. 1) extending from pipe 54 and opening into pipe 50at a location intermediate piloted relief valve 49 and check valve 63,and a check valve 97 is interposed in pipe 96 to permit flowtherethrough only in the direction toward pipe 50.

From the above description of the centrifugal drive it embodying thepresent invention it will be apparent that hydraulic motor 4-2 caneffect the high speed forward rotation of basket 45 during the normalspinning operation of the basket by disposing valve 55 in the positionillustrated in FIG. 3. vi hen the solids in the basket charge have beendried to the desired extent, the control valve 55 can be moved manuallyor otherwise to the position of FIG. 4, at which time the piloted reliefvalve 35 is unloaded to drop the pressure in the pipe 34, while thepiloted relief valve 49 closes and builds up to the pressure for whichit is set, at which point valve 4% blows to the tank 12 the hydraulicfluid pumped by the pump 1'7 and by the hydraulic motor 42 acting as apump. The pressure maintained in pipe 5!) by relief valve 49 is a backpressure on motor 42 causing the latter to exert a braking torque on thecentrifugal basket. When the centrifugal basket 45 comes to rest, pump17 continues to supply fluid under pressure to motor 42 by way of hose52, pipe 5% and either the sequentially operated adjustable flow controlvalves 61 and 62 (FIG. 1) or the continuously adjusted flow controlvalve 6!. (FIG. 6). Further, as previously explained, the parallelconnected adjustable flow control valves 61 and 62, when operated insequence by the sequence valve as, or the single flow control valve 61which is adjusted by actuating device '76, tend to maintain a constantspeed of rotation of basket 35 in the reverse direction. Thus, thecentrifugal 44 may be provided with a discharger of the kind disclosedin United States Letters Patent No. 2,667,974, which is more fullyidentified here inabove, and wherein the discharger shoe is continuouslymaintained within the basket 45 and extends generally in the directionof the normal high speed rotation of the basket so that it cannot diginto the wall of solids in the basket during such high speed rotation,but can dig into the wall of solids for effecting the discharge thereofthrough the bottom opening of the basket only during the controlled, lowspeed reverse rotation of the centrifugal basket.

Although the hydraulic drive 10 is shown with its motor 42 connected tothe lower end of the basket shaft of a link suspended centrifugal, it isto be understood that hydraulic drives embodying this invention can beused with other types of centrifugals, for example, machines of theoverhead suspended type or the like.

In the centrifugal drives 10 illustrated in FIGS. 1 and 6, separatepumps 16 and 17 provide the flows of hydraulic fluid under pressureemployedfor high speed forward rotation of the basket 45 and for brakingand slow speed reverse rotation of the basket, respectively, but asingle pump can be employed to perform the functions of pumps in and 17.Thus, in the centrifugal drive illustrated diagrammatically in FIG. 8and there generally identified by the reference numeral 100, theelectric motor 111 has its shaft 113 connected by a coupling 114 to theshaft 119 of a variable volume, vane type pump 116 which may be of thekind previously described with reference to the pump 13?, and whichdraws fluid from the supply tank 112 through inlet pipe 132, while theoutlet of pump 116 delivers hydraulic fluid under pressure to a pipe 133which extends to a housing 156 of a distributing or control valve E55.Also extending from the valve housing 155 are a pipe 134 connected by acoupling 139 to a flexible pipe or hose 146 extending to the inlet 141of a hydraulic motor M2 which may be the same as the motor 42 of FIG. 1and is similarly adapted for direct coupling to a centrifugal basket(not shown), and a pipe 150 connected by a coupling 151 to a flexiblehose or pipe 152 extending rorn the outlet 143 of motor 142. Further, areturn pipe 137 extends from valve housing 156 back to the hydraulicfluid supply tank 112.

Valve 155 further includes a valve body or spool 158 which is axiallyslidable in housing 156 and has a rod 159 projecting from one end of thehousing to permit the valve spool to be selectively disposed in thecentral position of FIG. 8, or in and toward the left, respectively,from the position of FIG. 3.

The spool 158 of control valve 155 may have two axially spaced apartannular recesses ing a narrow central land 2% from lands 201 and 2th, atthe opposite ends of the spool, and such recesses and lands are disposedalong the spool in relation to the positions where conduits 133, 134,237 and 150 open into housing 156 so that, when spool 153 is in itscentered position, as shown in FIG. 8, recesses 193 cation between allof the conduits 133, 134, 137 and 15%. Thus, when spool 153 is in itsillustrated centered position, the output of pump 3.16 is dumped back totank 112 through pipe 137, and hydraulic fiuid can circulate freely toand from motor E42 through pipes 134 and 159, so that the centrifugalbasket either remains at rest, or coasts if the basket is in a state ofrotation when the valve is moved to the position of FIG. 8.

When valve spool 15% is displaced toward the right from thepositionshown in FIG. 8, pipes 133 and 1 34 communicate with each other acrossrecess 1% and 137 communicate with each other across recess 199, so thatthe output of pump lid is fed by way of pipes 133 and 13d and hose tomotor 142- to cause forward rotation of the latter, while the exhaustedfluid is returned from the motor to tank 112 by way of hose 152 andpipes 15% and 137.

When valve spool 158 is displaced toward the left from the positionillustrated in FIG. 8, pipes 133 and communicate with each other acrossthe recess 199, and pipes 134 and 137 communicate with each other acrossthe recess 138, so that the output of pump 116 is fed, by way of pipes133 and 150 and hose 152 to motor 142 in order to cause reverse rotationof the latter, while the exhausted positions displaced toward the rightI 298 and 3.99 separatand 199' establish communiand pipes 1 1 fluid isreturned from the motor to tank 112 by way of hose 141 and pipes 134 and137.

As shown in FIG. 8, the hydraulic centrifugal drive 1019 furtherincludes a pressure relief valve 135 interposed in pipe 134 for limitingthe maximum pressure in the latter, and being effective to dumphydraulic fluid to the return pipe 137 by way of a branch pipe 136whenever the pressure in pipe 134 exceeds the value for which thepressure relief valve is set. The pipe 151 also has a pressure reliefvalve 149 interposed therein for limiting the maximum pressure of thehydraulic fluid in that pipe, and valve 149 is eflective to dumphydraulic fluid from pipe 150 into pipe 134 by way of a branch pipe 132whenever the pressure in pipe 151) exceeds the predetermined value forwhich valve 149 has been set.

Hydraulic fluid under pressure is supplied to motor 142 through pipe 134to effect forward rotation, and through pipe 156 to effect reverserotation, and the pressure relief valves 135 and 149 are respectivelyset to permit a higher pressure in pipe 151 than in pipe 134, so that agreater braking torque will be available to bring the centrifugal basketto rest or to a desired relatively low speed of rotation after forwardrotation of the basket at high speed.

In order to provide the small rate of flow of hydraulic fluid underpressure to motor 142 necessary for eflecting the slow reverse rotationof the latter, pipes 164 and 165 by-pass a portion of pipe 150 locatedbetween pressure relief valve 149 and hose 152, and a check valve 163 isinterposed in the by-passed portion of pipe 151? and permits flowtherethrough only in the direction from the motor back to the valve 155,whereas flow toward motor '142 can only occur through the bypass pipes.The bypass pipes 164 and 165 have an adjustable flow control valve 161interposed therebetween in order to provide the necessary throttling ofthe flow for the desired slow reverse rotation of motor 142.

Since motor 142 has increasing leakage with increasing loads on motor142 during the slow reverse rotation of the latter, it is necessary toincrease the rate of flow of hydraulic fluid under pressure through hose152 to motor 142 in order to maintain a substantially constant speed ofslow reverse rotation of motor 142 with increasing loads on the latter.For this purpose, the hydraulic centrifugal drive 100 of FIG. 8 includesa single adjustable flow control valve 161 which, as in the modificationof FIG. 6, is operated by an actuating device 176 having a pressuresensing connection 177 to the pipe 165 at the downstream side of flowcontrol valve 161, so that the pressure of the hydraulic fluid fed tomotor 142 during reverse rotation acts in actuating device 176 tofurther open flow control valve 161 in response to an increasingpressure, that is, in accordance with increasing loads on motor 142.

Hydraulic drive 101) further includes a check valve 187 interposed inpipe 133 to permit flow through the latter only in the direction frompump 116 to valve 155, and thereby protect pump 116 from back pressuresthat are higher than its rated pressure, for example, the braking orback pressure occurring in pipe 133 when valve 155 is shifted to theposition for reverse rotation or braking of motor 142 while the motorand the basket driven thereby are undergoing forward rotation.

A check valve 188 is interposed in the pipe 162 to permit flow throughthe latter only in the direction from relief valve 14-9 to pipe 134, anda spring loaded check valve 175 is interposed in the return pipe 137 topermit flow through the latter in the direction toward tank 112.

When valve 155 is shifted to the braking and reverse rotation positionwhile the basket driven by motor 142 is undergoing high speed rotationin the forward direction, motor '142 acts as a pump which builds uppressure through check valve 163 against relief valve 149', and thelatter limits this back pressure causing the motor to exert a brakingtorque. An excess back pressure of hydraulic fluid is dumped by valve149 through check valve 188 to pipe 134 to maintain an adequate supplyof hydraulic fluid at the inlet 141 of motor 142, thereby to preventcavitation in the motor. The spring loaded check valve 175 in returnpipe 137 establishes a suflicient resistance to the flow of hydraulicfluid through the return pipe back to the tank to overcome the flowresistance of check valve 188 causing a pressure drop across the latter,and thereby ensures that the hydraulic fluid passing through check valve183 will travel along pipe 134 in the direction toward motor 142, ratherthan in the opposite direction through. pipe 134 and return pipe 137 tothe tank.

Although the arrangement illustrated in FIG. 8 has the advantage overthe arrangement shown in FIG. 1 of eliminating the auxiliary pump 17 ofthe latter, this advantage is obtained at the expense of providing aclosed circuit for the hydraulic fluid flowing through motor 142 duringbraking of high speed forward rotation, so that difficulties may beexperienced in the dissipation of heat from the limited volume ofhydraulic fluid circulating rapidly through the closed braking circuitand thus having an insufficient time for adequate cooling by radiationduring each passage through the closed braking circuit. Further, whentwo pumps are provided, as in the embodiment of FIG. 1, the auxiliarypump 17 may be selected so as to provide a substantially higher pressureof hydraulic fluid than the rated pressure of the main, variable volumepump 16, thereby to provide a maximum torque for relatively slow reverserotation of the centrifugal basket, for example, during discharging ofthe latter.

Referring to FIGS. 1, 6 and 8, it will be seen that the hydraulic drivesembodying this invention may be further provided with a difl'erentialpressure responsive switch 263, for example, of the type that iscommercially available under the designation Barksdale No. 532-9, whichis operated by a difference between the pressures at the opposite sidesof the check valve 63 or 163, as sensed in pipes 294 and 295. The switch203 controls an electrical circuit 206 that includes a battery or otherelectrical source 2117 and a signal 208, for example, a lamp, which isenergized only when a predetermined pressure drop is sensed by switch263. During forward rotation of motor 42 or 142, the return flow throughpipe 5% or 150 passes through check valve 63 or 163 so that thedifferential pressure or pressure drop necessary for operating switch293 is not then available. However, during reverse rotation of themotor, check valve 63 or 163 blocks the direct flow of hydraulic fluidunder pressure through the pipe or 150 and causes the flow of hydraulicfluid under pressure to be diverted through the bypass containing thetwo flow control valves 61 and 62 (FIG. 1) or the single continuouslyadjusted flow control valve 61 or 161 (FIGS. 6 and 8), and the flowcontrol valve or valves produce a pressure drop of the order necessaryfor operating the differential pressure responsive switch 263 when themotor 42 or 142 is turning in the reverse direction at a predeterminedslow speed which is safe for discharging, thereby energizing the signal263 to indicate that conditions safe for discharging have been attained.

Referring now to FIG. 9 which illustrates a modification of a portion ofthe hydraulic drive shown in FIG. 8, it is to be understood that theremainder of the drive may be the same as that in FIG. 8. In themodification of FIG. 9, the distributing or control valve a has itsspool 158a which is movable within the valve housing 156a formed with amiddle land 266a which is not centered between the end lands 201a and262a, so that the annular recess 193a has a greater axial length thanthe annular recess 199a. By reason of the above, the spool 1585:, whenin its central position shown in FIG. 9, establishes communicationbetween the conduit 133 carrying hydraulic fluid from the outlet of thesingle pump and the conduits 134 and 137, by way of annular recess 198a,while the lands 266a and 2412 close otf the communications between theconduit 156 and the conduits 133 and 137, respectively. When valve spool153a is shifted toward the right from the position of FIG. 9, conduit150 is communicated with return conduit 137 by way of annular recess199a, while annular recess 198a establishes communication betweenconduits 133 and 134 and land 201a blocks the port at the a-diacent endof housing 155a opening into conduit 137. On the other hand, when valvespool 158a is shifted toward the left from the position shown in FIG. 9,annular recess 19% establishes communication between conduits 133 and154 and annular recess 153a establishes communication between conduits 134 and 137.

Further, the modified hydraulic drive illustrated in FIG. 9 has conduits136 and 154 extending from the pressure relief valves 135 and 149 to thereturn conduit 137 and through which the respective pressure reliefvalves dump hydraulic fluid back to the tank or reservoir when thepressures acting on the relief valves exceed adjustably predeterminedvalues. in order to prevent cavitation in the motor 142 during operationof the latter as a pump upon continued rotation of the motor in eitherthe forward or reverse direction at a time when the control valve 155ais positioned for reverse or forward rotation, respectively, themodified drive of FIG. 9 further includes check valves 174- and 137which correspond to the check valves 74 and 97, respectively, of thedrive shown in PEG. 1. Check valves 174 and 197 are respectivelyinterposed in conduits 173 and 15 6 which are branches of a conduitextending from the return conduit 154 and which open into the conduits134 and 1511, respectively, at a location between pressure relief valve135 and the motor and at a location between the pressure relief valve149 and the bypass conduit 164 extending from conduit 150, respectively.

The modification of FIG. 9 further includes a cooling device 193 whichreplaces the check valve 175 of FIG. 8 and which corresponds to thecooling device 93 of the modification illustrated in FIG. 6. The coolingdevice 193 has a cooling coil 135 interposed in its housing 194 so as toprovide a suitable restriction in the return flow of hydraulic fluid tothe storage tank by way of the return conduit 137.

The modified hydraulic drive illustrated in FIG. 9 operates as follows:

When valve spool 158:; is displaced toward the right from the centralposition illustrated in FIG. 9, hydraulic fluid under pressure passesfrom the pump through conduit 133 and conduit 134 to the motor of thecentrifugal, while the discharge from the motor passes through conduit150 into conduit 137 for return to the tank so that the motor is drivenat a relatively high speed in the forward direction. If valve spool158:: is returned to its illustrated central position while the motor isstill being rotated in the forward direction by the inertia of thebasket attached thereto, communication between conduits 151 and 137 byway of valve 155a is blocked, thereby building up the pressure acting onrelief valve 149 which limits the pressure for obtaining a predeterminedbraking torque, while the excess pressure of hydraulic fluid is dumpedback to the tank through conduits 154-, 13s and 137. During such brakingof the forward rotation of the motor, the hydraulic fluid is cooled bypassage through the cooling device 193 during its return to the storagetank. Further, by reason of the fact that conduits 133, 13 1- and 137are all communicated with each other through valve 155a when the latteris in the position of FIG. 9, fresh hydraulic fluid is continuouslyadded to the braking circuit from conduit 133- to conduit 134, but suchadded fluid is not under pressure as a result of the communication ofconduits 133 and 134 with return conduit 137. Thus, the problem ofexcessive heating of the hydraulic fluid circulating within a closedbraking loop or circuit as mentioned above in connection with thedescription of the hydraulic drive of FIG. 8 is substantially avoided.

During braking of the forward rotion of the motor, the check valve 174permits additional hydraulic fluid to be drawn into conduit 134 fromconduit 154 so as to ensure an adequate supply of hydraulic fluid to themotor acting as a pump for avoiding cavitation in the latter.

If spool 158a remains in the central position illustrated in FIG. 9after forward rotation of the motor has been halted in the mannerindicated above, the motor will remain at rest by reason of the factthat hydraulic fluid under pressure carried from the pump by conduit 133is dumped back to the storage tank by way of conduit 137. Further, ifvalve spool 15% is disposed in the central position of FIG. 9 duringrotation of the motor in the reverse direction, the fluid dischargedfrom, the motor through conduit 134 can pass without resistance throughvalve 155a into return pipe or conduit 137, while a free circulation offluid to the motor occurs through conduits 137, 136, 154, 196 andthereby permitting the motor to coast in the reverse direction. Whenvalve spool 158a is displaced toward the left from the positionillustrated in FIG. 9, fluid under pressure passes from conduit 133through the valve into conduit 150- for supply to the motor by way ofthe continuously adjustable flow control valve 161 (FIG. 8), while thedischarge from the motor flows through conduit 134 and valve a into thereturn conduit 137.

Referring to FIG. 10, it will be seen that the further modification ofthe hydraulic drive of FIG. 8 which is there illustrated employs adistributing or control valve 155 having the same construction as thevalve 155 of FIG. 8, but simplifies the drive by using a single pressurerelief valve 235 which is interposed in conduit 133 extending from thesingle pump to the control or distributing valve and being operative todump hydraulic flu d from conduit 133 through a conduit 236 to thereturn conduit 137 when the pressure in conduit 133- exceeds anadjustably predetermined value. Further, in the drive of FIG. 10, thecheck valves 174 and 197, which are provided to prevent cavitationduring a power failure while the motor is rotating in the forward orreverse directions, respectively, are interposed in conduits whichbranch off from a common connection to the conduit 236 and open into theconduits 134 and 150, respectively.

The modified drive of FIG. 10 operates as follows:

The central position of spool 15% of vlave 155 establishes communicationbetween all of the conduits 133, 134, 137 and 150 so that, if the motoris at rest, it will continue in that condition, or if the motor isrotating in the forward or reverse direction, it will continue to coastin that same direction.

When spool 158 is displaced toward the right from the central positionof FIG. 10, conduits 133 and 134- communicate with each other throughvalve 155 which simultaneously establishes communication betweenconduits 150 and 137 so that hydraulic fluid under pressure issupcharged fluid is carried away from the motor through conduit 15%,thereby effecting forward rotation of the motor. If the motor isrotating in the reverse direction when the valve. 155 is positioned forforward rotation, the

motor acts as a pump backing up a pressure of hydraulic fluid throughconduits 134 and 133 to the pressure relief valve 235, and the latterdumps the excess pressure of fluid through conduits 236 and 137 back tothe storage tank or reservoir, thereby determining the braking torquewhich is applied for halting the reverse rotation. At the same time,check valve 197 permits hydraulic fluid to flow from conduit 236 intoconduit 150 in order to ensure an adequate supply of hydraulic fluid tothe motor which then acts as a pump during braking of the reverserotation.

When a spool 158 is displaced toward the left from i the centralposition of FIG. 10, communication is established between conduits 134-and 137 and between conduits 133 and 1511, thereby to supply fluid underpressure 1 to the motor in the direction for effecting reverse rotationthereof. If the motor is undergoing high speed rotation in the forwarddirection at the time when valve spool 153 is disposed in the positionfor reverse rotation, the motor acts as a pump and backs up pressurethrough conduit 15%) and conduit 133 so that relief valve 235 once againlimits the maximum pressure, and thereby determines the braking torqueavailable for halting forward rotation of the motor. At the same time,check valve 174 permits fluid to flow from conduit 236 into conduit 134for ensuring an adequate supply of fluid to the motor acting as a pumpduring braking of the forward rotation.

Referring now to FIG. 11, it will be seen that the hydraulic drive thereillustrated is a further modification of the drive of FIG. 1 includingthe features previously described with reference to FIG. 6, and with thedrive being arranged so that the outputs of pumps 16 and 17 can be usedin parallel to provide an increased rate of flow of hydraulic fluid tothe motor 42 during rotation of the latter in the forward direction.Such increased rate of flow to the motor 42 can be used for achievinghigher rotational speeds of the motor, or for supplying hydraulic fluidunder pressure to larger motors which develop increased torque forfaster acceleration of the driven basket or for easier discharging ofsolids from the latter.

In the hydraulic drive illustrated in FIG. 11, and there generallyidentified by the reference numeral 360, the various parts correspondingto those previously described with reference to FIGS. 1 and 6 areidentified by the same numerals. The drive 306 includes a conduit 301having a check valve 72 and a pressure gauge 76 interposed therein andextending from the outlet of auxiliary pump 17 to the central port ofthe distributing or control valve 55. A conduit 302 extends from theoutlet of the main variable delivery pump 16 to the piloted relief valve35 and has a check valve 303 interposed therein to permit flow throughconduit 302 only in the direction from pump 16 toward piloted reliefvalve 35. As in FIG. 1, a conduit 34 extends from piloted relief valve35 for connection to the normal inlet 41 of the hydraulic, positivedisplacement motor 42, and a pipe 36 is also connected to piloted reliefvalve 35 and opens into a return pipe 37 extending back to tank 12 andin which a cooler 93 is interposed for the purposes previously describedin detail with reference to FIG. 6.

A pipe 304 extends from one of the delivery ports of valve housing 56and connects to the conduit 302, with a check valve 365 being interposedin pipe 304 to permit flow through the latter only in the direction fromvalve 55 toward piloted relief valve 35. The pilot line 38 for pilotedrelief valve 35 extends from the latter to pipe 304 at a location alongthe latter intermediate distributing valve 55 and check valve 305.

The other delivery port of valve housing 56 is connected by a pipe 396to the piloted relief valve 49 and a check valve 3t'l7 is interposed inpipe 306 to permit flow through the latter only in the direction towardthe related piloted relief valve. The pilot line 53 of relief valve 49extends from the latter back to the pipe 306 at a location along thelatter between check valve 307 and distributing valve 55. A conduit 50extends from piloted relief valve 49 for connection to the normal outlet43 of motor 42, and has the check valve 63 interposed therein to permitflow therethrough only in the direction from the motor towards reliefvalve 49, and, as in the modification of FIG. 6, check valve 63 isby-passed by pipes 64 and 65 having the flow control valve 61 interposedtherebetween and being continuously adjusted by the actuating device 76which responds to the pressure sensed in conduit 50 through a sensingconnection 77.

Hydraulic fluid dumped by the piloted relief valve 49 is led from thelatter through a pipe 54 to the return conduit 37. As in the drive ofFIG. 1, the drive shown in FIG. 11 further includes check valves 74 and97 interposed in conduits 73 and 96 which extend between the returnconduit 37 and the conduits 34 and 56, respec- 16 tively, in order toensure an adequate supply of hydraulic fluid at the normal inlet 41 andthe normal outlet 43, respectively, of motor 42 either during continuedforward or reverse rotation of the motor following a power failure, orduring braking of the forward or reverse rotation of the motor bypositioning of spool 58 of distributing valve 55 in the position forreverse rotation or in the position for forward rotation, respectively.

The above described hydraulic drive illustrated in FIG. 11 operates asfollows:

When spool 58 of control or distributing valve 55 is in its illustratedcentral position, the pipes or conduits 3G1, 304 and 306 are all incommunication with the drain conduit 57 extending from the valve housing56 to the return conduit 37 so that the output of pump 17 is returned totank 12 and the pilot lines 38 and 53 of piloted relief valves 35 and 49are both vented to the tank. Thus, the unloaded piloted relief valve 35dumps the output of main pump v16 back to the tank 12 by way of pipes 36and 37 and the motor 42 remains at rest if it is initially in thatcondition. Since piloted relief valve 49 is also unloaded, the motor 42will coast in either the forward or reverse direction upon dispositionof valve spool 58 in its illustrated central position.

When spool 58 is displaced toward the right from the central positionillustrated in FIG. 11, conduit 331 is placed in communication with pipe304 so as to feed the output of auxiliary pump 17 through pipe 304 whichopens into conduit 302 so that the combined flows of pumps 16 and 17then pass through conduit 34 to the normal inlet 41 of motor 42. Whenpipe 394 is connected to conduit 301, as previously described, pilotedrelief valve 35 is loaded through pilot line 38, and thereby establishesa predetermined maximum pressure for the hydraulic fluid in conduit 34.The displacement of spool 58 toward the right also establishescommunication between pipe 306 and the return or drain conduit 57 sothat pilot line 53 of relief valve 49 is vented to the tank, whereby thehydraulic fluid discharged from the normal outlet 43 of motor 42 iscarried by conduit 50 through check valve 63 to relief valve 49 and isdumped by the latter through conduit 54 and return conduit 37 back totank 12. Accordingly, motor 42 is then rotated in the forward directionby the combined flows of pumps 16 and 17.

If spool 58 is disposed in the above described position for forwardrotation of pump 42 at a time when the latter is rotating in the reversedirection, so that motor 42 then operates as a pump, the loaded pilotedrelief valve 35 determines the maximum pressure permitted in conduit 34,and thereby establishes the braking torque for halting rotation in thereverse direction, while fluid is supplied by way of conduit 50 to thenormal outlet 43 through the loaded relief valve 35 and check valve 97in order to avoid cavitation in motor 42. Similarly, in the event of apower failure while the motor is rotating in the reverse direction,fluid is supplied by way of conduit 50 to the normal motor outlet 43through the unloaded relief valve 35 and check valve 97.

When spool 58 is displaced toward the left from the central position ofFIG. 1'1, communication is established between conduit 391 and pipe 306,thereby loading piloted relief valve 49 by way of its pilot line 53 andfeeding the flow from pump 17 through the adjustable flow control valve61 to the normal outlet 43 of motor 42. At the same time, pipe 304 isvented to the tank thereby unloading piloted relief valve 35 so that thedischarge from motor 42 during reverse rotation of the latter is dumpedby valve 35 through conduits 36 and 37 back to the tank 12, and theoutput of the main variable delivery pump 16 is also dumped through theunloaded relief valve 35 back to the tank.

If spool 58 of valve 55 is placed in its position for reverse rotation,as described above, at a time when the motor 42 is rotating in theforward direction, whereby 17 the motor acts as a pump, the loadedpiloted relief valve 49 establishes the maximum pressure in conduit 50,and thereby determines the braking torque, while fluid is supplied tothe normal inlet 41 of the motor through the unloaded piloted reliefvalve 35 and the check valve 74 in order to prevent cavitation in themotor by reason of an inadequate supply of fluid. In the event of apower failure while the motor is rotating in the forward direction,fluid pumped by the motor 42 acting as a pump spills over the unloadedrelief valve 49 and passes via conduits 54 37 and 73 and check valve 74into conduit 34 from where it is supplied to the inlet 41 of the motorto prevent cavitation therein.

The hydraulic drive of FIG. ll further preferably includes unloadingvalves 3438 and 3% which are respectively interposed in the conduits 361and 392 respectively extending from the outlets of pumps 17 and 16, andwhich are operative to unload one of the pumps until the full deliveryor output of the other pump has been utilized by the hydraulic motor 42.Valves capable of performing the above mentioned operations of valves30% and 309 are commercially available from Denison EngineeringDivision, American Brake Shoe Company, Columbus, Ohio, under thedesignations RJGdl-E06A and RJ101E06A, respectively. The unloadingvalves 3638 and 3&9 automatically dump back to the tank 12 theunutilized outputs of the respective pumps, thereby reducing the peakload on the electric motor driving the pumps and also reducing theheating of the circulated hydraulic fluid. If the unloading valves 3%and 309 are not used in the drive of FIG. 11, the variable delivery mainpump 16 will automatically adjust back to Zero delivery, and the excessoutput of the fixed volume auxiliary pump will be dumped back to thetank by piloted relief valve 35 until the motor has accelerated thecentrifugal basket up to about 20% of its rated forward speed.

It will be apparent from the above that hydraulic drives embodying thepresent invention are capable of driving a centrifugal basket with ahigh speed in the forward direction reached by either a constanthorse-power or constant torque acceleration, which is determined byselection of the governor spring 27 of pump 16, and further that thedrives embodying this invention are capable of driving the basket at anadjusted relatively low speed in the reverse direction, which low speedis continuously maintained even during a varying load on the basket, forexample, during discharging of solids therefrom. Further, the describedhydraulic drives provide exclusively hydraulic braking of either forwardor reverse rotation of the motor down to rest, and also protect themotor against any damage due to cavitation either during braking or inthe event of a power failure.

Although illustrative embodiments of the invention have been describedin detail herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments, and that various changes and modifications may be effectedtherein without departing from the scope or spirit of the invention,except as defined in the appended claims.

What is claimed is:

l. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a load such as a centrifugal basket for driving the latter,first and second conduit means connected to said motor and forming acircuit through which hydraulic fluid can travel to and from said motorin opposite directions for effecting forward and reverse rotation ofsaid motor, a prime mover, pumping means driven by said prime mover todeliver hydraulic fluid under pressure to said circuit, first and secondpressure relief means interposed in said first and second conduit means,respectively, between said pumping means and said motor and operative tolimit the pressures motor in the direction corresponding to reverserotation of hydraulic fluid in each of said conduit means to apredetermined value by dumping fluid therefrom, means operable tointerrupt the supply of fluid to said motor through one of said conduitmeans while the motor is rotating in the direction efiected by travel offluid thereto through that conduit means and simultaneously to increasethe pressure in said other conduit means above said predetermined value,and means operative upon the interruption of the supply of fluid throughsaid one conduit means to supply to that conduit means and thence tosaid motor an amount of the fluid being dumped by the pressure reliefmeans in said other conduit means suiiicient to prevent cavitation insaid motor as it continues to rotate in the last named direction due tothe momentum of the load on said motor.

2. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a centrifugal basket for driving the latter, conduit meansconnected to said motor and forming a circuit through which hydraulicfluid can circulate to and from said motor in opposite directions foreffecting forward and reverse rotation of said motor, a prime mover,pumping means driven by said prime mover and delivering hydraulic fluidunder pressure to said circuit, control means selectively determiningthe direction of circulation of hydraulic fluid through said circuitfrom said pumping means, means restricting the rate of flow of hydraulicfluid through said circuit to the motor in the direction correspondingto reverse rotation of the motor, thereby to cause relatively slowreverse rotation, and means operative in response to a predeterminedpressure drop across said restricting means correspending to apredetermined speed of reverse rotation of said motor to generate asignal indicating that that predetermined speed has been attained.

3. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a centrifugal basket for driving the latter, conduit meansconnected to said motor and forming a circuit through which hydraulicfluid can circulate to and from said motor in opposite directions foreffecting forward and reverse rotation of said motor, a prime mover,pumping means driven by said prime mover and delivering hydraulic fluidunder pressure to said circuit, control means selectively determiningthe direction of circulation of hydraulic fluid through said circuitfrom said pumping means, means restricting the rate of flow of hydraulicfluid through said circuit to the motor in the direction correspondingto reverse rotation of the motor, thereby to cause relatively slowreverse rotation, and means operative to increase the restricted rate offlow of the hydraulic fluid upon increased loading of said motor,thereby to compensate for increased leakage in the motor and tend tomaintain a substantially constant speed of reverse rotation.

4. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a centrifugal basket for driving the latter, conduit meansconnected to said motor and forming a circuit through which hydraulicfluid can circulate to and from said motor in opposite directions foreffecting forward and reverse rotation of said motor, a prime mover,pumping means driven by said prime mover and delivering hydraulic fluidunder pressure to said circuit, control means selectively determiningthe direction of circulation of hydraulic fluid through said circuitfrom said pumping means, means restricting the rate of flow of hydraulicfluid through. said circuit to the of the motor, thereby to causerelatively slow reverse rotation, and means responding to the pressurein said circuit between said motor and said restricting means toincrease said rate of flow with increasing pressure, thereby to tend tomaintain a constant speed of reverse rota- 13 tion as leakage in saidmotor increases With increasing load on the motor.

5. A hydraulic drive for centrifugals as in claim 4; wherein saidresponding means includes a servo-motor connected to said adjustablerestricting means and spring urged in the direction for decreasing saidrate of flow, and means transmitting said pressure in the circuit tosaid servo-motor to act in the =latter in the direction for increasingsaid rate of flow.

6. A hydraulic drive 'for centrifu-gals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a centrifugal basket for driving the latter, conduit meansconnected to said motor and forming a circuit through which hydraulicfluid can circulate to and from said motor in opposite directions 'foreffecting forward and reverse rotation of said motor, a prime mover,pumping means driven by said prime mover and delivering hydraulic fluidunder pressure to said circuit, control means selectively determiningthe direction of circulation of hydraulic fluid through said circuitfrom said pumping means, a plurality of adjustable flow control valvesconnected in parallel in said circuit to restrict the rate of flow ofhydraulic fluid through said circuit to said motor in the directioncorresponding to reverse rotation of the motor, thereby to causerelatively slow reverse rotation of the motor, and means sequentiallyincluding said flow control valves in said circuit in accordance withincreasing load on said motor, thereby to increase said rate of flow andtend to maintain a desired speed of reverse rotation as the leakage insaid motor increases with increasing load.

7. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a centrifugal basket for driving the latter, conduit meansconnected to said motor and ctorming a circuit through which hydraulicfluid can circulate to and from said motor in opposite directions forefiecting forward and reverse rotation of said motor, a prime mover,pumping means driven by said prime mover and delivering hydraulic fluidunder pressure to said circuit, control means selectively determiningthe direction of circulation of hydraulic fluid through said circuitfrom said pumping means, a plurality of adjustable flow control valvesconnected in parallel in said circuit to restrict the rate of flow ofhydraulic fluid to said motor in the direction corresponding to reverserotation of the motor, thereby to cause relatively slow reverse rotationof the motor, and normally closed sequence valve means connected inseries with one of said flow control valves to prevent the flow ofhydraulic fluid through said one flow control valve until the pressureof the flow of hydraulic fluid to the motor exceeds a predeterminedvalue, whereupon said sequence valve means opens to include said onecontrol valve in said circuit and increase said rate of flow forcompensating the increased leakage in said motor resulting fromincreased loading thereof.

8. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a centrifugal basket for driving the latter, conduit meansconnected to said motor and forming a circuit through which hydraulicfluid can circulate to and from said motor in opposite directions foreflecting forward and reverse rotation of said motor, a prime mover,pumping means driven by said prime mover and delivering hydraulic fluidunder pressure to said circuit, control means selectively determiningthe direction of circulation of hydraulic fluid through said circuitfrom said pumping means, check valve means in a portion of said circuitthrough which hydraulic fluid flows in the direction from said motorduring forward rotation of the latter and permitting flow through saidcheck valve means only in said direction from the motor, by-pass conduitmeans extending from said portion of the circuit around said check valvemeans, flow restricting means in said bypass conduit means to provide arestricted rate of flow therethrough -to the motor in the directioncorresponding to reverse rotation of said motor, thereby to ensurerelatively slow reverse rotation and means operative in response tovariations in the load on said motor to vary the rate of flow throughsaid restricting means in compensation for variations in the leakage inthe motor resulting from said load variations and thereby maintain thespeed of reverse rotation substantially constant.

9. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a centrifugal basket for driving the latter, conduit meansconnected to said motor and forming a circuit through which hydraulicfluid can circulate to and from said motor in opposite direction foreffecting forward and reverse rotation of said motor, a prime mover,pumping means driven by said prime mover and delivering hydraulic fluidunder pressure to said circuit, control means selectively determiningthe direction of circulation of hydraulic fluid through said circuitfrom said pumping means, pressure relief means interposed in saidcircuit between said pumping means and said motor to limit the pressuresof hydraulic fluid in said circuit acting on said motor, meansrestricting the rate of flow of hydraulic fluid through said circuit tothe motor in the direction for effecting reverse rotation of the motor,thereby to cause relatively slow reverse rotation and means operative inresponse to variations in the load on said motor to vary the rate offlow through said restricting means in compensation for variations inthe leakage in the motor resulting from said load variations and therebymaintain the speed of reverse rotation substantially constant.

10. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a centrifugal basket for driving the latter, conduit meansconnected to said motor and forming a circuit through which hydraulicfluid can circulate to and from said motor in opposite directions foreffecting forward and reverse rotation of said motor, a prime mover,pumping means driven by said prime mover and delivering hydraulic fluidunder pressure to said circuit, control means selectively determiningthe direction of circulation of hydraulic fluid through said circuitfrom said pumping means, pressure relief means interposed in saidcircuit between said pumping means and said motor to limit the pressuresof hydraulic fluid in said circuit acting on said motor, check valvemeans in a portion of said circuit through which the hydraulic fluidflows in the direction from the motor during forward rotation of thelatter and permitting free flow through said portion of the circuit onlyin said direction from the motor, by-pass conduit means extending fromsaid portion of the circuit around said check valve means, flowrestricting means in said by-pass conduit means to provide a restrictedrate of flow therethrough to the motor in the direction for reverserotation of the latter, thereby to ensure relatively slow reverserotation, and means operative in response to variations in the load onsaid motor to vary the rate of flow through said restricting means incompensation for variations in the leakage in the motor resulting fromsaid load variations and thereby maintain the speed of reverse rotationsubstantially constant.

11. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a centrifugal basket for driving the latter, a prime mover,variable volume pumping means driven by said prime mover, relativelyhigh pressure pumping means driven by said prime mover, a tank forcontaining hydraulic fluid to be delivered under pressure by each ofsaid pumping means, first and second conduit means extending betweensaid variable volume pumping means and said motor and between said highpressure pumping means and said motor, respectively, and alternatelycarrying fluid under pressure to and from said motor for effectingforward and reverse rotation of said motor, piloted pressure reliefvalve means in each of said conduit means having a loaded condition, inwhich said valve means determines the maximum pressure in the relatedconduit means, and an unloaded condition, in which the valve means dumpsthe output of the related pumping means back to said tank, and controlvalve means operative selectively to unload one of said pressure reliefvalve means while loading the other of said pressure relief valve means,and to unload said other pressure relief valve means while loading saidone pressure relief valve means.

12. A hydraulic drive for centrifugals as in claim 11; furthercomprising return pipe means extending from said pressure relief valvemeans to said tank for returning the hydraulic fluid dumped by saidpressure relief valve means, and a connecting pipe means extending fromsaidreturn pipe means to said first conduit means at a location alongthe latter between the related pressure relief valve means and saidmotor, and a check valve in said connecting pipe means permitting flowthrough the latter in the direction toward said first conduit means, sothat, in the event of a failure of said prime mover While said motor isrotating in the forward direction, said first conduit means can drawfluid from said return pipe means to ensure that a sufiicient supply offluid is available to the motor for preventing cavitation.

13. A hydraulic drive for centrifugals as in claim 12; furthercomprising a spring loaded check valve in sai return pipe meanspermitting flow through the latter in the direction toward said tank andimposing a resistance to such flow toward the tank which is greater thanthe flow resistance of said check valve in said connecting pipe means.

14. A hydraulic drive for centrifugals as in claim 12; furthercomprising a cooling device including a housing interposed in saidreturn pipe means, and a cooling coil in said housing adapted to have acoolant circulated the-rethrough for cooling the liow of hydraulic fiuidpassing through said return pipe means and said housing, said coolingcoil interposing a resistance to the fiow through said housing which isgreater than the resistance of said check valve in said connecting pipemeans.

15. .A hydraulic drive for centrifugals as in claim 12; furthercomprising additional connecting pipe means extending irom said returnpipe means to said second conduit means at a location along the latterbetween the related pressure relief valve means and said motor andhaving a check valve interposed therein to permit flow through saidadditional connecting pipe means only in the direction toward saidsecond conduit means, so that, in the event of a failure of said primemover while said motor is rotating in the reverse direction, said secondconduit means can draw fluid from said return pipe means to ensure thatan adequate supply of fluid is available to the motor for preventingcavitation.

16. A hydraulic drive for centrifugals as in claim 11; wherein saidsecond conduit means has a check valve interposed therein to permit flowtherethrough only in the direction from said motor to the pressurerelief valve means in said second conduit means; and further comprisingbypass conduit means connected to said second conduit means around saidcheck valve in the latter so that fluid under pressure can flow throughsaid bypass conduit means in the direction toward said motor foreffecting reverse rotation of the latter, and flow restricting meansinterposed in said bypass conduit means to limit the rate of flowtherethrough and thereby provide a relatively slow speed of reverserotation.

17. A hydraulic drive for centrifugals as in claim 16; wherein said flowrestricting means includes a plurality of adjustable flow control valvesconnected in parallel in said bypass conduit means, and normally closedsequence valve means connected in series with one of said flow controlvalves to prevent the flow of hydraulic fluid through said one flowcontrol valve, said sequence valve means opening in response to theexceeding of a predetermined pressure in said second conduit meansbetween said motor and check valve, thereby to permit flow through saidone flow control valve for increasing the rate of flow of fluid throughsaid bypass conduit means to said motor in order to compensate forincreased leakage in the motor upon increased loading of the latter.

18. A hydraulic drive for centrifugals as in claim 16; wherein said flowrestricting means includes an adjustable fiow control valve, andactuating means for said flow control valve responsive to the pressurein said second conduit means between said check valve in the latter andsaid motor to decrease the flow restricting effect of said flow controlvalve upon increases in said pressure, thereby to compensate for theincreased leakage in the motor resulting from increased loads formaintaining a substantially constant speed of reverse rotation.

. 19. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a centrifugal basket for driving the latter, a prime mover,variable volume pumping means driven by said prime mover, a tankcontaining hydraulic fluid to be delivered under pressure by saidpumping means, control valve means connected to said pumping means toreceive the fluid under pressure delivered by the latter, first andsecond conduit means extending from said control valve means to saidmotor and alternately carrying hydraulic fluid to and from said motorfor effecting forward and reverse rotation of the latter, return pipemeans extending from said control valve means to said tank, said controlvalve means having a forward drive position in which said pumping meansand first conduit means are connected while said second conduit meanscommunicates with said return pipe means, a braking and reverse driveposition in which said pumping means is connected to said second conduitmeans while said first conduit means communicates with said return pipemeans and a rest and coasting position in which said pumping means isconnected to said return pipe means while said first and second conduitmeans communicate with each other and means in said second conduit meansoperative in response to fluid pressure in that conduit means in excessof a predetermined value to dump from that conduit means to said firstconduit means fluid in an amount sufficient to limit'the pressure insaid second conduit to said valve, so that when said control valve meansis moved to said braking and reverse drive position while said motor isrotating in the forward direction said pressure responsive meansdetermines the back pressure in said second conduit means acting on saidmotor to produce a braking torque and fluid is dumped by said pressureresponsive means to'said first conduit means whence it is supplied tosaid motor to prevent cavitation therein.

20. A hydraulic drive for centrifugals as in claim 19; furthercomprising a first pressure relief valve in said first conduit means,saidpressure responsive means including a second pressure relief valvein said second conduit means.

21. A hydraulic drive for centrifugals as in claim 20; said pressureresponsive means further including a branch pipe extending from saidsecond pressure relief valve to said first conduit means at a. locationalong the latter between said first pressure relief valve and said motorto receive hydraulic fluid dumped by said second pressure relief valvewhen the pressure in said second conduit means becomes excessive, and acheck valve in said branch pipe permitting flow through the latter onlyin the direction toward said first conduit means, so that, when saidcontrol valve means is moved to said braking and reverse drive positionwhile said motor is rotating-in the forward direction, said secondpressure relief valve deter- 23 mines the back pressure in said secondconduit means acting on said motor to produce a bnaking torque, andfluid is supplied to said first conduit means and said motor from saidsecond pressure relief valve by way of said branch pipe.

22. A hydraulic drive for centrifugals as in claim 21; furthercomprising a spring loaded check valve in said return pipe meansestablishing a resistance to flow in the latter which is greater thanthe flow resistance of said check valve in the branch pipe, thereby toensure that fluid will travel along said first conduit means from saidbranch pipe to said motor rather than to said control valve means whenthe latter is disposed in said braking and reverse drive position whilesaid motor is rotating in the forward direction.

23. A hydraulic drive for centrifugals comprising:

a positive displacement reversible rotary hydraulic motor adapted to bedirectly coupled to a centrifugal basket for driving the latter;

a prime mover;

variable volume pumping means driven by said prime mover;

a tank containing hydraulic fluid to be delivered under pressure by saidpumping means;

control valve means connected to said pumping means to receive the fluidunder pressure delivered by the latter;

first and second conduit means extending from said control valve meansto said motor and alternately carrying hydraulic fluid to and from saidmotor for effecting forward and reverse rotation of the latter;

return pipe means extending from said control valve means to said tank;

said control valve means having a forward drive position in which saidpumping means and first conduit means are connected while said secondconduit means communicates with said return pipe means,

a braking and reverse drive position in which said pumping means isconnected to said second conduit means while said first conduit meanscommunicates with said return pipe means,

and a rest and coasting position in which said pumping means isconnected to said return pipe means while said first and second conduitmeans communicate with each other;

first and second pressure relief valves in said first and second conduitmeans, respectively, for limiting the pressure of hydraulic fluid in therelated conduit means;

a check valve in said second conduit means permitting flow through thelatter only in the direction from said motor to said second pressurerelief valve;

a bypass conduit connected to said second conduit means around saidcheck valve in the latter so that flow can occur through said bypassconduit [in the direction toward said motor during reverse rotation ofthe latter;

and flow restricting means in said bypass conduit for providing arelatively slow speed of reverse rotation of said motor.

24. A hydraulic drive for centrifugals as in claim 23; wherein said flowrestricting means is adjustable; and further comprising actuating meansfor said adjustable flow restricting means operative in response toincreases in the pressure in said second conduit means between saidcheck valve and said motor to cause said flow restricting means topermit an increased rate of flow to the motor, thereby to compensate forincreased leakage occurring in the motor with increased loading andtending to maintain a substantially constant slow speed of reverserotation.

25. A hydraulic drive for centrifugals as in claim 24; wherein saidactuating means includes a servo-motor having a movable member connectedto said adjustable flow restricting means and being spring urged in thedirection for decreasing the rate of flow of fluid through said flowrestricting means, and means connecting said servo-motor to said secondconduit means so that said pressure in the second conduit means betweensaid check valve and said motor acts in the servo-motor against saidmovable member to displace the latter in the direction for increasingthe rate of flow through said flow restricting means.

26. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a centrifugal basket for driving the latter, conduit meansconnected to said motor and forming a circuit through which hydraulicfluid can travel to and from said motor in opposite directions foreffecting forward and reverse rotation of the motor, a prime mover,first and second pump means driven by said prime mover to respectivelydeliver relatively large and small flows of hydraulic fluid, and valvemeans disposed between said pump means and said circuit in a position toreceive the flow from both of said pump means and operative in oneposition thereof to deliver the combined flows of said first and secondpump means through said circuit in the direction for forward rotation ofthe motor, in another position thereof to deliver the relatively smallflow of said second pump means through said circuit in the direction forreverse rotation of the motor while diverting the flow of said firstpump means to a fluid reservoir, and in a third position thereof todivert the flow of both of said pumps to said fluid reservoir.

27. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a load such as a centrifugal basket for driving the latter, aprime mover, first and second pump means driven by said prime mover torespectively deliver relatively large and small flows of hydraulicfluid, a tank for containing hydraulic fluid to be delivered underpressure by said pump means, first and second conduit means extendingfrom said motor to alternately carry fluid under pressure to and fromsaid motor for effecting forward and reverse rotation of said motor,first and second piloted pressure relief valves connected to said firstand second conduit means, respectively, and each having a loadedcondition, in which said relief valve determines the maximum pressure inthe related conduit means, and an unloaded condition, in which therelief valve dumps the hydraulic fluid received thereby back to saidtank, means conducting the flow of fluid from said first pump means tosaid first piloted relief valve, and control means operative, in oneposition, to direct the flow from said second pump means to said secondpiloted relief valve and, in another position, to direct said flow fromthe second pump means to said first piloted relief valve, each of saidpiloted relief valves assuming said loaded condition thereof only inresponse to said flow from said second pump means so that, with saidcontrol means in said one position, said flow from the second pump meansis delivered through said second conduit means to said motor to causereverse rotation of the latter and, with said control means in saidother position, the combined flows of said first and second pump meansare delivered through said first conduit means to said motor to causeforward rotation of the latter.

28. A hydraulic drive for centrifugals as in claim 27; wherein saidsecond conduit means has a check valve interposed therein to permit flowtherethrough only in the direction from said motor to the pressurerelief valve means in said second conduit means; and further comprisingbypass conduit means connected to said second conduit means around saidcheck valve in the latter so that fluid under pressure can flow throughsaid bypass conduit means in the direction toward said motor foreffecting reverse rotation of the latter, and flow restricting meansinterposed in said bypass conduit means to limit the rate of flowtherethrough and thereby provide a relatively slow speed of reverserotation.

29. A hydraulic drive for centrifugals as in claim 27; wherein saidsecond conduit means has a check valve interposed therein to permit flowtherethrough only in the direction from said motor to the pressurerelief valve means in said second conduit means; and further comprisingbypass conduit means connected to said second conduit means around saidcheck valve in the latter so that fluid under pressure can flow throughsaid bypass conduit means in the direction toward said motor foreffecting reverse rotation of the latter, flow restricting meansinterposed in said bypass conduit means to limit the rate of flowtherethrough and thereby provide a relatively slow speed of reverserotation and means operative in response to variations in the load onsaid motor to vary the rate of flow through said restricting means incompensation for variations in the leakage in the motor resulting fromsaid load variations and thereby maintain the speed of reverse rotationsubstantially constant.

30. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a centrifugal basket for driving the latter, a prime mover,pumping means driven by said prime mover, a tank containing hydraulicfluid to be delivered under pressure by said pumping means, controlvalve means connected to said pumping means to receive the fluid underpressure delivered by the latter, first and second conduit meansextending from said control valve means to said motor and alternatelycarrying hydraulic fluid to and from said motor for eifecting forwardand reverse rotation of the latter, return pipe means extending fromsaid control valve means to said tank, and first and second pressurerelief valves in said first and second conduit means, respectively, forlimiting the pressures of hydraulic fluid in the related conduit means,said control valve means having a forward drive position in which saidpumping means communicates with said first conduit means and said secondconduit means communicates with said return pipe means, a reverse driveposition in which said pumping means communicates with said secondconduit means and said first conduit means communicates with said returnpipe means, and a braking position in which said second conduit means isblocked, so that said second pressure relief valve determines themaximum pressure in said second conduit means for braking forwardrotation of the motor, and in which said pumping means communicates withsaid first conduit means and said return pipe means to dump the pressureof said pumpingmeansback to said tank while ensuring an adequate supplyof relatively cool hydraulic fluid from said tank to the motor throughsaid first conduit means.

31. A hydraulic drive for centrifugals comprising a positivedisplacement, reversible rotary hydraulic motor adapted to be directlycoupled to a centrifugal basket for driving the latter, a prime mover,pumping means driven by said prime mover, a tank containing hydraulicfluid to be delivered under pressure by said pumping means, controlvalve means connected to said pumping means to receive the fluid underpressure delivered by the latter, first and second conduit meansextending from said control valve means to said motor and alternatelycarrying hydraulic fluid to and from said motor for efifecting forwardand reverse rotation of the latter, return pipe means extending fromsaid control valve means to said tank, pressure relief valve meansinterposed in the connection between said pumping means and said controlvalve means to limit the pressure of hydraulic fluid in said connection,and connecting pipe means extending between said pressure relief valvemeans, said return pipe means and said first and second conduit meansand having check valve means therein to permit flow from said connectingpipe means into said first and second conduit means, said control valvemeans having a forward drive position in which said pumping means andfirst conduit means are connected while said second conduit meanscommunicates with said return pipe means, a, reverse drive and brakingposition in which said pumping means communicates with said secondconduit means and said first conduit means communicates with said returnpipe means, while said pressure relief valve means determines themaximum pressure in said second conduit means for braking of for wardrotation of the motor, and a rest and coast position inwhich saidpumping means, said first and second conduit means and said return pipeall communicate with each other.

32. A hydraulic drive for centrifugals comprising:

a positive displacement reversible rotary hydraulic motor adapted to bedirectly coupled to a centrifugal basket for driving the latter;

a prime mover;

first and second pumping means driven by said prime mover;

a tank for containing hydraulic fluid to be delivered under pressure byeach of said pumping means;

first and second conduit means extending between said first pumpingmeans and said motor and between said second pumping means and saidmotor, respectively, and alternately carrying fluid under pressure toand from said motor for effecting forward and reverse rotation of saidmotor;

piloted pressure relief valve means in each of said conduit means havinga loaded condition in which said valve means determines the maximumpressure in the related conduit means,

and an unloaded condition in which the valve means dumps the fluidcarried to it through the related conduit means back to said tank;

and control valve means operative selectively to unload one of saidpressure relief valve means while loading the other of said pressurerelief valve means,

and to unload said other pressure relief valve means while loading saidone pressure relief valve means.

33. A hydraulic drive for centrifugals as in claim 27:

each of said relief valves in its loaded condition determining themaximum pressure in the related conduit means by dumping'fluid to saidtank;

and further comprising means operative, when the fluid supply to saidmotor through one of said conduit means is interrupted with the motorrotating in the direction effected by delivery of fluid thereto throughthat conduit means, to supply to that conduit means and'thence to saidmotor an amount of the fluid bemg dumped by saidpressure relief valvesto said tank suflicient to prevent cavitation in said motor as the motorcontinues to rotate in said direction due to the momentum of said load.

34. A hydraulic drive for centrifugals as in claim 15:

further comprising a check valve in said return pipe means allowing flowtherethrough only in the direct1on toward said tank,

said check valve in said return pipe means imposing a resistance to flowtherepast which is greater than that imposed by the check valve ineither of said connecting pipe means.

35. A hydraulic drive for centrifugals as in claim 15:

wherein said second conduit means has a check valve interposed thereinto permit flow therethrough only in the direction from said motor to thepressure relief valve means in said second conduit means;

and further comprising bypass conduit means connected to said secondconduit means around said check valve in the latter so that fluid underpressure can flow through said bypass conduit means in the directiontoward said motor for effecting reverse rotation of the latter,

and flow restricting means interposed in said bypass conduit means tolimit the rate of flow therethrough and thereby provide a relativelyslow speed of reverse rotation. 36. A hydraulic drive for centrifugalsas in claim 22: wherein said second conduit means has a check valveinterposed therein to permit flow therethrough only in the directionfrom said motor to the pressure relief valve means in said secondconduit means; and further comprising bypass conduit means connected tosaid second conduit means around said check valve in the latter so thatfluid under pressure can flow through said bypass conduit means in thedirection toward said motor for effecting reverse rtation of the latter,and flow restricting means interposed in said bypass conduit means tolimit the rate of flow therethrough and thereby provide a relativelyslow speed of reverse rotation. 37. A hydraulic drive for centrifugalsas in claim 30: said second pressure relief valve determining the saidmaximum braking pressure in said second conduit by dumping fluid fromthat conduit to said tank; and further comprising means operative as theforward rotation of the motor is being braked to deliver to said firstconduit means an amount of the fluid being dumped by said secondpressure relief valve sufficient to prevent cavitation of the motor. 38.A hydraulic drive for centrifugals as in claim 30: wherein said secondconduit means has a check valve interposed therein to permit flowtherethrough only in the direction from said motor to the pressurerelief valve in said second conduit means; and further comprising bypassconduit means connected to said second conduit means around said checkvalve in the latter so that fluid under pressure can flow through saidbypass conduit means in the direction toward said motor for effectingreverse rotation of the latter, and flow restricting means interposed insaid bypass conduit means to limit the rate of flow therethrough andthereby provide a relatively slow speed of reverse rotation. 39. Ahydraulic drive for centrifugals as in claim 37: further comprisingbypass conduit means extending from said second pressure relief valve tosaid tank to receive the fluid dumped by that valve,

said bypass conduit means having a flow restrictor therein; saidoperative means including branch conduit means extending from saidbypass conduit means at a location along the latter between said secondpressure relief valve and said restrictor to said first conduit means ata location along the latter between said first pressure relief valve andsaid motor and having a check valve therein permitting fluid flow onlytoward said first conduit means;

said restrictor imposing a greater resistance to the flow of liquidtherepast than is imposed by said check valve so that as the forwardrotation of the motor is being braked an amount of the fluid beingdumped by said second pressure relief valve is supplied to said firstconduit means to prevent cavitation in said motor. 40. A hydraulic valvefor centrifugals as in claim 31: wherein said second conduit means has acheck valve interposed therein to permit flow therethrough only in thedirection from said motor to the control valve means; and furthercomprising bypass conduit means connected to said second conduit meansaround said check valve in the latter so that fluid under pressure canflow through said bypass conduit means in the direction toward saidmotor for effecting reverse rotation of the latter,

and flow restricting means interposed in said bypass conduit means tolimit the rate of flow therethrough and thereby provide a relativelyslow speed of reverse rotation.

41. A hydraulic drive for centrifugals as in claim 26:

further comprising unloading valve means interposed in said circuit andoperative with said control valve disposed in said one position tounload one of said pump means until the full output of the other of saidpump means is being utilized by the motor whereby to reduce the peakload on said prime mover as well as the heating of the circulatedhydraulic fluid.

42. A hydraulic drive for centrifugals comprising:

a positive displacement reversible rotary hydraulic motor adapted to bedirectely coupled to a centrifugal basket for driving the latter;

a prime mover;

separate relatively high capacity pumping means and relatively lowcapacity pumping means both driven by said prime mover;

a tank containing hydraulic fluid to be delivered under pressure by saidpumping means;

conduit means extending between said pumping means and said motor andforming a circuit through which hydraulic fluid can travel to and fromsaid motor in opposite directions for effecting forward and reverserotation thereof and to which both of said pumping means continuouslydeliver fluid when said prime mover is operating;

and means including a control Valve and operable in one position of saidcontrol valve to dump the entire ouput of said low capacity pumpingmeans from a location in said conduit means ahead of said motor to saidtank while directing the output of said high capacity pumping meansthrough said conduit means to said motor in a direction to producerelatively rapid forward rotation thereof,

and operable in another position of said control valve to dump theentire output of said high capacity pumping means from a location insaid conduit means ahead of said motor to said tank while directing theoutput of said low capacity pumping means through said conduit means tosaid motor in a direction to produce relatively slow reverse rotationthereof.

43. A hydraulic drive for centrifugals comprising:

a positive displacement reversible rotary hydraulic motor adapted to bedirectly coupled to a centrifugal basket for driving the latter;

a prime mover;

pumping means driven by said prime mover;

a tank containing hydraulic fluid to be delivered under pressure by saidpumping means;

a control valve;

means for carrying hydraulic fluid from said pumping means to saidcontrol valve;

first and second conduit means extending from said control valve to saidmotor for carrying hydraulic fluid to and from said motor in oppositedirections for effecting forward and reverse rotation thereof;

piloted pressure relief valve means in each of said conduit means,

each of said pressure relief valve means having a loaded condition inwhich it determines the maximum pressure in the related conduit means,

and an unloaded condition in which it dumps the fluid carried to itthrough the related conduit means to said tank;

said control valve being operable selectively to load said first reliefvalve and unload said second relief valve while directing the fluid delivered to it from said pumping means through said first conduit means,

and to load said second relief valve and unload said first relief valvewhile directing the fluid delivered to it from said pumping meansthrough 5 said second conduit means.

References Cited in the file of this patent UNITED STATES PATENTSHuguenin Oct. 27, 1931 10 Ferris et al May 30, 1933

2. A HYDRAULIC DRIVE FOR CENTRIFUGALS COMPRISING A POSITIVEDISPLACEMENT, REVERSIBLE ROTARY HYDRAULIC MOTOR ADAPTED TO BE DIRECTLYCOUPLED TO A CENTRIFUGAL BASKET FOR DRIVING THE LATTER, CONDUIT MEANSCONNECTED TO SAID MOTOR AND FORMING A CIRCUIT THROUGH WHICH HYDRAULICFLUID CAN CIRCULATE TO AND FROM SAID MOTOR IN OPPOSITE DIRECTIONS FOREFFECTING FORWARD AND REVERSE ROTATION OF SAID MOTOR, A PRIME MOVER,PUMPING MEANS DRIVEN BY SAID PRIME MOVER AND DELIVERING HYDRAULIC FLUIDUNDER PRESSURE TO SAID CIRCUIT, CONTROL MEANS SELECTIVELY DETERMININGTHE DIRECTION OF CIRCULATION OF HYDRAULIC FLUID THROUGH SAID